A personal identification number (PIN) is a numeric password associated with a user, and the PIN may be used to authenticate the user. Typically, the user is authenticated by entering a number that matches the PIN associated with the user. The PIN may be a four-digit number in the range 0000-9999, resulting in 10,000 possible PINs, but PINs of other lengths and/or using other characters (e.g., letters and/or symbols) may be used. The user has a 0.01% (10−4) probability of guessing a four-digit PIN with a single guess. A PIN-based verification system may allow a user to make multiple attempts, increasing the likelihood that the user will guess a correct PIN. For example, if the user is allowed three attempts to input a 4-digit PIN, the user will have a 0.03% (3×10−4) probability of correctly guessing the correct PIN.